The present invention relates to combustion systems, and more particularly to a regenerative burner designed to operate utilizing two chemically different oxidizing gases supplied into the combustion chamber of a burner wherein during at least part of operation one of said two oxidizing gases is supplied cyclically throughout the regenerator and is preheated by recovered heat previously stored in the regenerator.
Regeneration has been utilized since the 1850s for the recovery of heat from exhaust gases in a variety of high temperature combustion processes, such as glass melters and open hearths. The regenerative principle involves utilizing heat storage beds located on opposite sides of a furnace through which, on an alternating basis, furnace flue gases are exhausted, thereby transferring heat to the bed. This heat is recovered from the heat storage beds by blowing combustion air through each of the storage beds, also on an alternating basis.
The application of regenerative burner systems has been broadened in recent years to such areas as industrial heating and aluminum melting by the development of compact regenerative burner systems. This compact system utilizes two small burners, each containing a refractory bed for heat storage.
While the use of regeneration has substantially increased the energy efficiency of a variety of high temperature continuous heating processes, the systems currently in operation have faced a series of limitations when applied in batch charge applications. A primary problem has been a limitation of furnace productivity due to the deficiency in the ability of regenerative burners to transfer heat during the initial stages of a melting or heating process when the furnace is charged with a cold load.
Heat transfer from regenerative burners is limited because of their inability to provide a high velocity impinging flame. This results in limited contact between the load being heated and the hot combustion products produced from the regenerative burners located above the scrap pile. Only the top portions of the scrap pile are involved in intensive convective and radiative heat transfer from the flame, and the remainder of the pile is shielded from the flame. The exhaust gases enter the regenerative beds at very high temperatures even when the majority of the surface of the scrap pile is cold.
This deficiency in heat transfer necessitates raising the furnace atmosphere to temperatures sufficiently above product temperatures to cause the furnace refractory to radiate heat to the load. Raising the temperature of the furnace atmosphere results in the deterioration of furnace components and an increase in the temperature of flue gases exhausted from the furnace, and may also result in rapid oxidation of the load. The overall effect typically is a loss of yield.
Another problem is the rapid decline in system efficiency during operation due to plugging of the regenerative beds by solid dust particles and condensable volatiles carried with the flue gases. This plugging inhibits the flow of flue gases through the bed and reduces the capacity of the regenerative bed to recover heat. The plugging also results in reduced combustion air flow and therefore loss of firing capacity.
There exists, therefore, a need for a regenerative combustion system and a method which results in more efficient heating and melting, particularly in batch charge operations.
There also exists a need for a regenerative system and method which results in maximization of furnace throughput with a given regenerative bed heat recovery capacity.
There exists a further need for a system and method which reduces the problem of regenerative burner plugging.
There exists a still further need for a regenerative system and method which can utilize both burners to provide strong, high temperature impinging flames for the rapid melt down of materials and which can take advantage of the high level of energy recovery which can be provided by regeneration without reducing the furnace production rate.